1. Field of the Invention
The present invention relates to media copy protection, and more particularly, to digital media copy protection method and system being able to prevent any unauthorized access to a digital media data set using a hybrid cryptographic technique.
2. Discussion of the Related Art
Communication systems such as computer networks, telecommunication systems, and other systems are increasingly using cryptography for the security of information. There are two main classes of cryptographic systems: symmetric key and public key cryptographic systems. In a symmetric key cryptographic system, a symmetric secret key is used for both of data encryption and decryption processes. There are several efficient implementations of the symmetric key cryptographic system, but the actual key managements of such implementations are often troublesome.
On the other hand, in a public key cryptographic system, the data encryption and decryption processes are independent from each other. That is, the data encryption process requires a public key, often designated as e, while the data decryption process requires a different (but mathematically related) private key d. Therefore, an entity being possessed of the public key may encrypt a plaintext, which is the original form of a message, but the entity may not be able decrypt a ciphertext, which is the encrypted form of the message.
If an entity selects a public key and publishes the public key, anyone is able to use the key to encrypt one or more messages for the entity. Then the entity keeps his private key secret so that he or she is the only one who can decrypt the ciphertexts of the messages. The implementations of the public key cryptographic systems are currently less efficient than those of the symmetric key cryptographic systems, but they are much safer.
In a hybrid cryptographic system, a plaintext is encrypted with a symmetric key corresponding to a symmetric algorithm. The symmetric key is then encrypted with a public key having a public algorithm. When a receiver receives the public key-encrypted symmetric key and the symmetric key-encrypted data, the receiver initially decrypts the symmetric key by using his own private key. Subsequently, the receiver decrypts the encrypted data by using the decrypted symmetric key. The processes of obtaining the original data in a hybrid cryptographic system are usually faster than those of the public key cryptographic system. In addition, a hybrid cryptographic system may allow using a different symmetric key each time, considerably enhancing the security of the symmetric algorithm. For that reason, the hybrid cryptographic systems are ideal for transferring the protected media data safely to a receiver.